The present invention relates to a method of severing vitreous or vitrocrystalline sheet material along predetermined lines, particularly by applying severing forces of thermal origin to the sheet material by irradiating it with at least one laser beam. The invention also relates to an apparatus for the performance of the method.
The term "vitrocrystalline material" used herein denotes material formed by thermally treating glass to cause the formation of one or more crystalline phases therein.
It is known that vitreous sheet material can be severed by irradiating the material with a laser beam. Thus United Kingdom Pat. specification No. 1,246,481 describes a method of severing vitreous sheet material by irradiating the material with a CO.sub.2 laser. Such a laser is selected because it has a wavelength such that its energy is very strongly absorbed by the vitreous material. In consequence of this energy absorption, thermomechanical stresses are created in the sheet material which cause it to fracture.
This known method is applicable only to a limited range of sheet material thicknesses. In particular, the method is not reliably applicable for severing vitreous sheets above 5 mm in thickness. Moreover in the practice of the known method the sheet material sometimes fractures along lines which depart from the line traced by the laser beam.